Effect of cholesterol oxidation products on cholesterol metabolism in the laying hen

Two experiments were conducted to determine the effect of purified cholesterol and oxidized cholesterol in the diet of the laying hen on egg production characteristics, in vitro - in ovo utilization of acetate for cholesterol biosynthesis, and the activity of hepatic 3-hydroxy-3-methylglutaryl coenzyme A reductase, the rate-limiting enzyme in biosynthesis of cholesterol. Previous work has demonstrated inhibition of cholesterol synthesis by cholesterol oxides in tissue culture cells but not in hepatic tissues of animals through dietary administration. Feeding .5% of either purified or oxidized cholesterol had no effect on egg production, egg weight, body weight, or diet consumption. In both experiments egg yolk cholesterol was significantly increased by both cholesterol sources, but eggs from hens fed oxidized cholesterol had lower cholesterol contents than those from hens fed purified cholesterol. Relative utilization of acetate for cholesterol biosynthesis was significantly reduced by feeding both cholesterol sources. Hepatic enzyme activity measured by production of mevalonic acid was significantly inhibited by feeding purified cholesterol. A further significant reduction in enzyme activity was observed when oxidized cholesterol was fed, indicating that dietary cholesterol oxides are much more potent than purified cholesterol in limiting the activity of the enzyme.